Reverberation method and system



` Dec. 2, 1947. M, RETT,NGER l k2,431,962

I REVERBERATION METHOD AND SYSTEM Filed Feb. 7, -1945 I 2 sheets-sheet 2 fly;

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/1772 may Patented Dec. 2, 1947 BEVERBERATION METHOD AND SYSTEM Michael 'Kettingen Encino, Caiif., assignor to Radio Corporation of America, a corporation of Delaware Application February 7, 194,5, Serial No. 57 6,6851

14 Claims.

This invention relates to sound recording VSystems, and particularly to a portion of a recording or rerecording system whereby sound is reproduced from a previously recorded record and modified in transmission before being again `recorded.

In the art of sound recordingand -rerecording, it well-known that `the characteristics of the signal may be modified in several aspects. The primary modification pertains tothe amplitude of one portion of the signal with respect to another, known as amplitude control, while asecond modincation relates to variations lin amplitude of the diifercnt frequencies in the same signal portion, known as equalization. An example oi the last mentioned Vnoodiiicatlon is where .cqualizing iilters creuse/d to reduce the vhigh frequency Components of a signal with respectto .the low frequency @mnonents thereof.

It frequently occurs, however, that it is desirable to ladd an entirely different quality to the sound, known as reverberation. For instance, a picture set Vmay represent a large hall, cave, or other enclosure which would have reverberation the sound were actually produced at the scene being depicted Vin the .picture However, the set is actually only abortion ef the actual scene. and the sound recorded therein has no appreciable reverberatioh. Thus, itisilecessary in the rerecording operation to .add reverberation. and it is to this feature of sound recording and rerecording that this .invention is directed. It is to be understood, `of course, that although the invention is shown in connection 'with a rerecording system, that it ris also applicable in the vdirect recording ofsound; that is, during the making of the original record. and also toradio broadcasting or direct reproductionas ign-public address systems.

` vTo add reverberation to the sound signal, one well-known method of and means 4for accomplishing-the result Vis to reproduce the-sound in a special chamber wherein the acoustic waves will be reiiected from Ithe variOllS surfaces of the chamber and then detected by a microphone and recorded or reproduced. A chamber of a given size and shane has a certain reverberation characteristie. The present invention is directed to -plural or dual reverberation chambers vwhich will provide a-pmultiplicity-of reverberation characteristics suitable for representing Ythe original sound from many types ,ofscenes ranging ,in ksize from a tiled shower bath to large railroad stations ,and caves. The chief feature of the chambers is that they have no parallel surfaces, while either chamber may be .utilized .separata/nor vlthe chambers Y2 may be interconnected through an adjustable door to provide a series of different reverberation characteristics. The adjustable door ,functions as a high pass iilter.

The principal object of the .inventiomtherefora is to facilitate the Vobtaining of different reverberation characteristcs in thek reproducton or recording of sound.

Another objectoi the invention is to provide an improved method of and system for obtaining various types :of reverberation characteristics.

A further object of the invention 4is to provide an improved reverberation System by the use of plural interconnected reverberation chambers.

A still Vfurther object of the invention is .to provide a method of and means lfor introducing reverberation into .a signal which may be varied during the actual transmission ofthe signal.

A still further object of the invention is to provide an improved method rof and means for obtaining a variable-high pass .acoustic filter.

Although the novel features `which are believed to be `characteristic of this invention will .be pointed out with particularity in the appended claims, the manner of its organization and the mode of its loperation will be better understood by referring to the `following ldescription read in conjunction with the accompanying drawings fo'ming a part hereof, vin which:

Fig. -1 is va diagrammatic View of a rerecording system utilizing a reverberationchamber embodying the invention.

Fig. 2 is awfplan View of the reverberatio-nchamber.

Fig. 3 is a diagrammatic elevational view of the reverberation chamber along the line 3-3 of Fig. 2 and showing the acoustic filter control feature.

Fig. 4 is a combination diagrammatic plan view of Aa reverberation chamber in one arrangement together with the reverberation characteristic obtainable with this arrangement. y

Fig. 5 is a combination view similar to Fig. 4 showing the reverberation characteristic obtainable with another arrangement of the chamber.

Fig. 6 is another combination of a reverberation chamber arrangement and the reverberation characteristic obtainable therefrom, and

Fig. 7 is another combination diagram showing a reverberation chamber arrangement together with its respective reverberation characteristic.

Referring now toAFig. 1, a source of sound is shown as a reproducer 5. the outbut of which iS connected to an amplifier 6 feedingr a mixer 1 connected to a recorder-.9 .through a Second .am-

plier 8. The output of the reproducer is also connected to reverberation chamber I0, the cutput of which is fed into the mixer 1. This is a representation of a basic rerecording system whereby all or any part of the output o the reproducer 5 may be transmitted through the reverberation chamber I!) before it is recorded at 9, it being understood that the source of signals may also be a microphone. It is also to be understood that a plurality of sources of signals may be simultaneously reproduced and recorded into a single record, one or more of the signals being reverberated in accordance with the nature of the source of sound being shown in the concomitant picture or in accordance with the story in a. radio broadcast program.

Referring now to Fig. 2, the outer walls of the dual reverberation chambers are constructed in the form shown by the trapezoid wherein a partition forms a trapezium chamber A and a trapezium chamber B, chamber B having a volume about twice that of chamber A. A preferred form is when chamber B is approximately 3000 cubic feet and chamber A is about i500 cubic feet. The walls of the chamber I are preferably of solid masonry= such as brick or concrete, of considerable thickness, so that when a door I2 in the partition, and of substantially the same thickness as the partition, is tightly closed` the sound in one chamber will not be transmitted to the other chamber. The door may be approximately six by eight feet. It will be noted that there are no parallel surfaces in either chamber, and in Fig. 3, it will be noted that the ceilings of the chambers are not parallel with the floors of the chambers.

Located in chamber A. a microphone I5 and a loud speaker I6 are shown diagrammatically, while in chamber B, a microphone I8 and a reproducer I9 are shown. it being understood that more than one microphone and more than one loud speaker may be employed if desired. It is also to be understood that special sound absorbing movable screens may be used in different positions in either chamber to produce special effects. Along the left-hand Wall of chamber A and extending over the major portion of its surface, as shown in Fig. 2, are a series of hinged panels 2| which have a hard surface on one side and a sound absorbing surface on the other side, and which are rotatable to expose either the hard surface or the sound absorbing surface to the sound waves. Any intermediate adjustment of the panels will provide an intermediate effect fro-m that obtained when the panels are in their eXtreme positions, as will be described hereinafter.

AsV mentioned above, the door I2 is of a thickness comparable to the walls and may have felt padding along its edges to prevent sound transmission therethrough when closed. However, the door is adjustable from a remote point, such as a mixer console from where it may be closed or opened to any amount desired to produce the proper reverberation characteristic as will be explained hereinafter. As shown in Fig. 3, the door I2 is mounted on a vertical shaft 23 having a gear 24 at the end thereof, the gear 24 being in mesh with a smaller gear 25 on the shaft of a motor 26. Energization of the motor 26 over conductors 21 will rotate the door I2 and either close it or open it to any desired extent by actuation of a reversing switch 30. In this manner, if the mixer does not believe the reverberation characteristic as indicated on his monitor is of the type desired, he

4 can vary it during the recording operation by actuation of the switch 3U.

Referring now to the specific types of characteristics obtainable with the above described dual chambers, reference s made to the remaining figures wherein Fig. 4 shows an arrangement wherein the microphone I5 in chamber A and the loud speaker I9 in chamber B are utilized to provide a characteristic having a greater reverberation time over the upper end of the audio spectrum than the lower end. This result is obtained because the door l2 functions as a high pass filter, thereby passing the high frequencies better than the low frequencies. Thus, the high frequencies will not only be reverberated in chamber A and pass through the door to speaker I9, but will also be further reverberated in chamber B to provide the characteristic shown in the graph in Fig. 4. It will be noted that the characteristic has a certain curvature which may be desirable to introduce into a signal originating in a certain type of scene.

In Fig. 5, the same microphone l5 is employed, but in cooperation with the speaker I6, both of which are located in the chamber A. In this instance, as shown by the graph by the solid line. a rising reverberation characteristic is also obtainable, but with the reversed curvature of that in Fig. 4. This characteristic results because the door I2 will more readily pass the high frequencies into chamber B wherein they will be reverberated, but they must again pass back through door I2 in order to reach the microphone I5. Thus, the high frequencies receive a greater reverberation than the low frequencies, but since they pass through the door I2 twice, the opposite curvature to that obtainable with the arrangement in Fig. 4 results. With the arrangement shown in Fig. 5, however, various positions of the door I2 from wide open condition to closed condition will vary the characteristic as shown by the dotted lines in the graph of Fig. 5.

Referring now to Fig. 6, both microphones I5 and I8 are illustrated together with their cooperative speakers I5 and I9. If only microphone I5 and speaker I6 are used, the reverberation characteristic will be as shown in curve A, and if only microphone I8 and speaker I9 are employed, a constant reverberation characteristic is obtained, as shown by curve B, but in which the reverberation time is higher because of the larger size of the chamber. These conditions, of course, obtain only when door I2 is closed. In this arrangement, either of the two cooperative microphones or speakers may be used individually or simultaneously to produce an intermediate reverberation characteristic between the chambers A and B, or each chamber may be used for separate signals in two recording channels. In each of the illustrations shown in Figs 4, 5, and 6, itis to be understood that the panels 2| are arranged so that the left-hand wall has a characteristic similar to the other inner surfaces; that is, the hard surfaces of the panels are exposed to the sound waves. By varying the angle of the panels, the characteristics shown in Figs. 4, 5, and 6 may be varied.

To illustrate the effect of the panels 2|, reference is made to Fig. 7 wherein the effect of using a microphone I8 and a loud speaker I9 is shown with the door I2 open and the panels 2| adjusted at an angle. With the panels adjusted to present the sound absorbing surfaces of the panels to the sound waves in chamber A, a drooping characteristic, such as shown by the solid line in Fig.

7, is obtained inasmuch as the high frequencies which are more readily passed through the door I2 are not returned to chamber B because of the absorption thereof by the panels 2|. By varying the opening of the door l2, various characteristics can be obtained, as illustrated by the dotted lines in Fig. '7.

From the above, it will be noted that the above described reverberation chambers are particularly exible from the standpoint of providing a multiplicity of reverberation characteristics; that is, from uniform characteristics to rising and drooping characteristics in various degrees. By the interconnection of the different microphones and loud speakers in the two chambers, adjustments of the door I2 and adjustments of the panels 2l, many different reverberation characteristics are obtainable. It is also possible to arrange in the chambers A and B temporary absorbing screens in case a special type of characteristic is to be produced. It is to be understood that instead of the dual chamber arrangement, three or more chambers may be interconnected by adjustable doors if characteristics not possible with dual chambers are desired.

In the above description, only the door l2 is described as controllable from without the chambers, but such a control may also be applied to the panel sections 2| so that they may be adjusted from a remote point such as the mixing console.

I claim as my invention:

1. A reverberation chamber system comprising outer wall sections, a floor section, a ceiling section, a partition between two wall sections to provide two separate chambers having no inner surfaces parallel, and a door in said partition to pass sound waves between said chambers.

2. A reverberation chamber in accordance with claim 1, in which adjustable panels are provided on the walls of at least one of said chambers for varying the sound absorbing characteristics in said chamber.

3. A reverberation chamber in accordance with claim 1, in which means are provided for adjusting the opening of said door.

4. A reverberation chamber system having a plurality of wall sections, a partition between two of said wall sections for dividing said chamber into two chambers having non-parallel inner surfaces, a door for passing sound Waves between said chambers, and means for remotely controlling the degree of opening of said door to control the acoustic coupling between said chambers.

5. A reverberation chamber system in accordance with claim Ll, in which a microphone is positioned in o-ne of said chambers, and a loud speaker is positioned in the other of said chambers, sound reproduced in one of said chambers being detected by the microphone in the other` of said chambers after passage through said door.

6. The method of obtaining a plurality of reverberation characteristics in a signal comprising reproducing said signal in a reverberation chamber, detecting said signal in another reverberation chamber, and varying the acoustic coupling between said chambers to vary the reverberation characteristic.

7. The method of obtaining a variation of a reverberation characteristic being introduced into a signal during the transmission of said signal comprising reproducing said signal in a reverberation chamber of a certain size, detecting said signal in another reverberation chamber of a size diiTerent from that of said first reverberation chamber, and varying the acoustic coupling between said reverberation chambers during the transmission of said signal.

8. The method of artificially modifying a sound produced in one location to correspond to the characteristic of said sound when produced in another location comprising reproducing said sound in a chamber having a certain reverberation characteristic, passing said sound through an acoustic filter into a chamber having a certain other reverberation characteristic, and detecting said sound in said second mentioned chamber.

9. The method in accordance with claim 8 in which said acoustic lter is adjustable during reproduction and detection of said sound.

10. The method of introducing different reverberation characteristics into a sound wave comprising reproducing said sound in a chamber having a certain reverberation characteristic, passing said sound through an acoustic lter into a chamber having a certain other reverberation characteristic, detecting said sound in said first mentioned chamber to provide one type of reverberation characteristic, and detecting said sound in said second mentioned chamber to provide a second type of reverberation characteristic.

11. The method in accordance with claim 10, in which said acoustic iilter is adjustable during reproduction and detection of said sound.

12. A reverberation system for sound waves comprising a plurality of chambers of diierent sizes, means for reproducing sound waves in any one of said chambers, means for detecting sound waves in any one of said chambers, and means for variably coupling said chambers acoustically to vary the reverberation time of certain frequencies in said sound waves with respect to certain other frequencies in said waves.

13. A reverberation system in accordance with claim 12, in which said last mentioned means includes an opening between chambers with means in said opening for varying the size thereof.

14. A reverberation system in accordance with claim 12, in which said last mentioned means includes an adjustable door between chambers and means for controlling the position of said door from a remote point.

MICHAEL RETTINGER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,675,102 Holland June 26, 1928 1,853,286 Round Apr. 12, 1932 2,318,417 Phelps May 4, 1943 2,037,363 Blanche Apr, 14, 1936 2,130,491 Gilliland Sept. 20, 1938 

